1. Field of the Invention
The invention relates to a hybrid fuel cell system. More particularly, the invention relates to an improvement of an electric power control method in a hybrid fuel cell system including an electric power storage device.
2. Description of the Related Art
In a conventional hybrid fuel cell system, in order to prevent over discharge/overcharge of a battery that is an electric power storage device, a remaining electric capacity of the battery is detected, and an amount of electric power generated by a fuel cell is adjusted, whereby a balance between charge and discharge in the battery is maintained.
An example of such a technology is a fuel cell power supply unit disclosed in Japanese Patent Laid-Open Publication No. 63-45765. In this fuel cell power supply unit, an amount of electric power remaining in a secondary battery and an electric current output from a fuel cell are detected, and the electric current output from the fuel cell is controlled in a feedback manner based on a set signal corresponding to the amount of electric power remaining in the secondary battery and a measurement signal corresponding to the electric current output from the fuel cell.
However, in the above-mentioned technology, the output electric current and a state of charge detected by sensors attached to the fuel cell and the secondary battery are used as the base information for control without being processed. Therefore, due to insufficient accuracy of the sensor and variation in the detected values obtained by the sensors, the information obtained by the sensors may differ from the actual information. If electric power control is performed based on the information having an error, an imbalance may be created between charge and discharge in the entire fuel cell system. Such an imbalance causes over discharge/overcharge of the secondary battery, and makes it difficult to maintain the optimum efficiency of the electric power generation in the entire system.